Liquid crystal display device

ABSTRACT

In a liquid crystal display device including a liquid crystal display panel and a backlight, the present invention provides a detection-use pixel having the same constitution as respective pixels constituting a liquid crystal display part in the liquid crystal display panel and being formed on a region other than the liquid crystal display part, a light detector detecting light from the backlight through the detection-use pixel, and a controller adjusting the intensity of the light from the backlight in response to a signal from the light detector to adjust the change of the characteristics and chromaticity in the liquid crystal display panel properly.

[0001] The present application claims priority from Japanese applicationJP2003-159277 filed on Jun. 04, 2003, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a liquid crystal display device,and more particularly to a liquid crystal display device which includesa backlight on a back surface of a liquid crystal display panel.

[0004] 2. Description of the Related Art

[0005] The liquid crystal display device is configured such thatrespective pixels of the liquid crystal display panel control opticaltransmissivities thereof and hence, the liquid crystal display device isusually provided with the backlight on the back surface of the liquidcrystal display panel.

[0006] Here, the liquid crystal display panel is configured such thateach pixel includes a pair of electrodes and the optical transmissivityof liquid crystal is controlled for each pixel in response to anelectric field generated between these electrodes.

[0007] With respect to the liquid crystal display panel having such aconstitution, there has been known a liquid crystal display panel inwhich liquid crystal thereof includes the temperature characteristicsand which includes means for adjusting a change of contrast in responseto the temperature characteristics (see Patent Document 1).

[0008] There has been also known a liquid crystal display panel in whichto prevent the occurrence of luminance irregularities on a surface of abacklight along with the large-sizing of the liquid crystal displaypanel, a plurality of light emitting diodes are used as the backlightand the liquid crystal display panel includes means which increases theluminance of the light emitting diodes at dark portions (see PatentDocument 2).

[0009] Further, there has been also known a liquid crystal display panelwhich includes a plurality of so-called white light emitting diodes as abacklight and also includes means which compensates for irregularitiesof chromaticity of the backlight (see Patent Document 3).

[0010] Patent gazettes the inventors of the present patent applicationreferred is identified as follows.

[0011] [Patent Document 1]

[0012] Japanese Unexamined Patent Publication: JP-A-7-301784

[0013] [Patent Document 2]

[0014] Japanese Unexamined Patent Publication: JP-A-2001-66569

[0015] [Patent Document 3]

[0016] Japanese Unexamined Patent Publication: JP-A-2001-209049

SUMMARY OF THE INVENTION

[0017] However, the liquid crystal display devices having suchconstitutions respectively must have means to solve the above-mentionedrespective drawbacks.

[0018] That is, there may be a case in which the characteristics and thechromaticity of the liquid crystal display panel are deviated from thecharacteristics and the chromaticity which are requested as finalproducts attributed to a cause that the color filter characteristics orthe liquid crystal characteristics of the liquid crystal display panelare changed or a cause that the chromaticity is changed attributed toirregularities of backlights or conditions such as temperature and thelike at the time of lighting the backlight. In such a case, it isnecessary to provide means which can overcome the drawbacks attributedto these causes and hence, the structure becomes complicatedunavoidably.

[0019] The present invention has been made under such circumstances andit is an object of the present invention to provide a liquid crystaldisplay device which can properly adjust the above-mentioned changes ofcharacteristics irrespective of the simple constitution thereof.

[0020] To briefly explain the summary of representative inventions amongthe inventions disclosed in this specification, they are as follows.

[0021] Means 1.

[0022] The liquid crystal display device according to the presentinvention is, for example, a liquid crystal display device including aliquid crystal display panel and a back light, wherein a detection-usepixel which has the same constitution as respective pixels constitutinga liquid crystal display part of the liquid crystal display panel isformed on a region other than the liquid crystal display part, and theliquid crystal display device further includes a light detector whichdetects light from the backlight through the detection-use pixel and acontroller which adjusts the intensity of the light from the backlightin response to a signal from the light detector.

[0023] Means 2.

[0024] The liquid crystal display device according to the presentinvention is, for example, a liquid crystal display device including aliquid crystal display panel for color display and a back light, theback light including a red light source, a green light source and a bluelight source, wherein a detection-use red pixel, a detection-use greenpixel and a detection-use blue pixel which have the same constitution asrespective pixels constituting a liquid crystal display part of theliquid crystal display panel are formed on a region other than theliquid crystal display part, and the liquid crystal display devicefurther includes a red light detector, a green light detector and a bluelight detector which detect light from the backlight through thedetection-use red pixel, the detection-use green pixel, thedetection-use blue pixel and a controller which adjusts the intensitiesof the red light source, the green light source and the blue lightsource of the backlight in response to signals from the light detectors.

[0025] Means 3.

[0026] The liquid crystal display device according to the presentinvention is, for example, on the premise of either one of the means 1and 2, characterized in that a frame having a display window whichexposes a liquid crystal display part of the liquid crystal displaypanel is arranged on an observation-side surface of the liquid crystaldisplay panel, and the detection-use pixel is covered with the frame.

[0027] Means 4.

[0028] The liquid crystal display device according to the presentinvention is, for example, on the premise of either one of the means 1,2 and 3, characterized in that the light detector is arranged on theobservation-side surface of the liquid crystal display panel.

[0029] Means 5.

[0030] The liquid crystal display device according to the presentinvention is, for example, on the premise of any one of the means 1 to3, characterized in that the light detector is arranged on a surface ofthe liquid crystal display panel opposite to the observation-sidesurface and, at the same time, a mirror is arranged on theobservation-side surface of the liquid crystal display panel in a statethat the mirror and the light detector sandwich the detection-use pixel.

[0031] Means 6.

[0032] The liquid crystal display device according to the presentinvention is, for example, on the premise of any one of the means 1, 2,3, 4 and 5, characterized in that the detection-use pixels are formed bymaking use of dummy pixels which are formed on peripheries of therespective pixels which constitute the liquid crystal display part.

[0033] Here, the present invention is not limited to the above-mentionedconstitutions and various modifications can be made without departingfrom the technical concept of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]FIG. 1 is a schematic constitutional view showing one embodimentof a liquid crystal display device according to the present invention;

[0035]FIG. 2 is a schematic constitutional view showing anotherembodiment of a liquid crystal display device according to the presentinvention;

[0036]FIG. 3 is a schematic constitutional view showing anotherembodiment of a liquid crystal display device according to the presentinvention; and

[0037]FIG. 4 is a schematic constitutional view showing anotherembodiment of a liquid crystal display device according to the presentinvention.

DETAILED DESCRIPTION

[0038] Embodiments of the liquid crystal display device according to thepresent invention are explained in detail in conjunction with drawingshereinafter.

[0039] Embodiment 1.

[0040]FIG. 1 is a constitutional view showing one embodiment of theliquid crystal display device according to the present invention.

[0041] First of all, there is provided a liquid crystal display panelPNL. The liquid crystal display panel PNL is configured such thatrespective substrates are arranged to face each other with liquidcrystal therebetween to form an envelope and the liquid crystal displaypanel PNL includes a Large number of pixels which are arranged in amatrix array in a spreading direction of the liquid crystal. A pair ofelectrodes is formed in each pixel and the liquid crystal is behaved inresponse to an electric field generated between respective electrodes soas to control the optical transmissivity of the liquid crystal.

[0042] Here, the electrodes are pulled out to the outside of theenvelope through respective signal lines and signals are supplied tothese signal lines from a liquid crystal driving driver DRV. That is, inresponse to the signals from the liquid crystal driving driver DRVthrough the signal lines, a given voltage is applied to the pair ofelectrodes of respective pixels thus performing a control of opticaltransmissivities of respective pixels independently from each other.

[0043] Further, the liquid crystal display device is configured suchthat a backlight BL is arranged on a back surface of the liquid crystaldisplay panel PNL as viewed from the observation side of the liquidcrystal display panel PNL and light from the backlight BL reaches eyesof a viewer through the respective pixels of the liquid crystal displaypanel PNL whose optical transmissivities are respectively controlled.

[0044] Here, the backlight BL is constituted such that, for example, reddiodes, green diodes and blue diodes are respectively arranged in amixed form on a plane parallel to the liquid crystal display panel PNL,wherein light which is a mixture of the these colors, that is, whitelight is irradiated to the liquid crystal display panel PNL side.

[0045] Further, the light intensities of the red diode, the green diodeand the blue diode of the back light BL are configured to beindependently controlled by a backlight control circuit LCC. Asdescribed above, the backlight BL is configured to produce the whitelight by emission of lights from respective diodes and to allow thewhite light to pass through the respective pixels of the liquid crystaldisplay panel PNL. However, to correct the change of chromaticity of theliquid crystal display panel PNL, the light emitting intensities of therespective diodes are configured to be adjusted by the backlight controlcircuit LCC.

[0046] On the other hand, the liquid crystal display panel PNL isconstituted as a liquid crystal display panel for color display, whereinwith respect to the respective pixels, for every three pixels which arearranged close to each other, one pixel is allocated to red, anotherpixel is allocated to green and the remaining pixel is allocated toblue. To be more specific, the color filters which are allocated torespective pixels are configured to be formed on a liquid-crystal-sidesurface of one of the substrates facing each other.

[0047] Further, a mass of these pixels constitute a liquid crystaldisplay part AR which displays an image thereon and a pixel fordetection (referred to as a detection-use pixel DP) which does notfunction as the liquid crystal display part AR is formed in a portion ofa periphery of the liquid crystal display part AR. The detection-usepixel DP is, for example, constituted of three detection-use pixels DP,wherein one detection-use pixel DP is allocated to red, anotherdetection-use pixel DP is allocated to green, and the remainingdetection-use pixel DP is allocated to blue. To be more specific, thecolor filters which are allocated to respective pixels are configured tobe formed on liquid-crystal-side surfaces of the respective substrates.

[0048] In view of the above-mentioned constitution, the pixels and thedetection-use pixels DP in the inside of the liquid crystal display partAR are formed in parallel at the time of manufacturing the liquidcrystal display panel PNL and these pixels have the samecharacteristics, that is, the same color filter characteristics, thesame liquid crystal characteristics and same other characteristics. Inother words, when the color filter characteristics of the pixels in theinside of the liquid crystal display part AR are changed, this change ismade in the substantially same mode as the change of the color filtercharacteristics of the detection-use pixels.

[0049] In the liquid crystal display panel PNL, in response to a signalfrom the liquid crystal driving driver DRV, an image is displayed on theliquid crystal display part AR in response to the signal. Here, theabove-mentioned three detection-use pixels DP are configured to alwayshave the maximum optical transmissivity.

[0050] Further, over the observation-side surface of the liquid crystaldisplay panel PNL, light detectors LDA are formed such that lightdetectors LDA respectively face the above-mentioned three detection-usepixels DP and outputs of the respective light detectors LDA are inputtedto the backlight control circuit LCC.

[0051] That is, in the liquid crystal display panel PNL, the states oflight transmission of the above-mentioned respective detection-usepixels DP which are formed under the same conditions as the respectivepixels of the liquid crystal display part AR are detected by the lightdetectors LDA. For example, when the detected chromaticity of thedetection-use pixel DP is displaced from the desired chromaticity, thelight emitting intensity of the diodes of color of the backlight BLcorresponding to the detection-use pixel DP is adjusted so as to makethe diodes hold the desired chromaticity. With respect to the backlightwhich generates the white light using the plurality of diodes whichdiffer in light emission colors, the chromaticities of the lightemission colors determine the purity of white (quality).

[0052] To be more specific, when it is detected that the red color isshifted from a given value based on the signal supplied from the lightdetector LDA which is arranged to face the detection-use pixel DP whichis allocated to the red color, the light emitting intensity of the reddiodes of the backlight BL is adjusted so as to make the red diodes holdthe desired chromaticity. Further, when it is detected that the greencolor is shifted from a given value based on the signal supplied fromthe light detector LDA which is arranged to face the detection-use pixelDP which is allocated to the green color, the light emitting intensityof the green diodes of the backlight BL is adjusted so as to make thegreen diodes hold the desired chromaticity. Still further, when it isdetected that the blue color is shifted from a given value based on thesignal supplied from the light detector LDA which is arranged to facethe detection-use pixel DP which is allocated to the blue color, thelight emitting intensity of the blue diodes of the backlight BL isadjusted so as to make the blue diodes hold the desired chromaticity.

[0053] Here, in FIG. 1, to the liquid crystal driving driver DRV,signals are supplied from the display control circuit DCC, for example.

[0054] In the liquid crystal display device having such a constitution,when the color filter characteristics or the liquid crystalcharacteristics of the liquid crystal display panel PNL are changed orthe chromaticity is changed due the irregularities of the backlight orconditions such as temperature at the time of lighting, it is possibleto obviate these changes and hence, it is possible to always hold thechromaticity in a stable manner.

[0055] In other words, when the optical transmissivity of any one ofdetection-use pixels DP is lowered due to, for example, the change ofcolor filter characteristics or liquid crystal characteristics, theirregularities of the backlight BL or the change of the backlight BLsuch as change of temperature at the time of lighting, the lightintensity of the light emitting diodes of the color corresponding to thedetection-use pixel DP is increased so as to compensate for an amount ofintensity of light corresponding to the lowering of contrast. To thecontrary, when the optical transmissivity of the detection-use pixel DPis higher than a proper value, to restore the proper contrast, the lightintensity of the light emitting diodes of the color corresponding to thedetection-use pixel DP is lowered. Accordingly, the liquid crystaldisplay device can always hold the display contrast which is notinfluenced by the change of optical transmissivities of the pixels.

[0056] In the above-mentioned embodiment, the detection-use pixels DPare formed on the region other than the liquid crystal display part ARexclusively or in a dedicated manner. However, with respect to theliquid crystal display panel PNL, there exists a liquid crystal displaypanel PNL which includes so-called dummy pixels which are different fromthe pixels arranged in the inside of the liquid crystal display part AR.It is needless to say that some of these dummy pixels are made tofunction as the above-mentioned detection-use pixels DP.

[0057] That is, in the liquid crystal display part AR, regions which aresurrounded by gate signal lines which extend in the x direction and arearranged in the y direction and drain signal lines which extend in the ydirection and are arranged in the x direction constitute pixel regions,wherein each pixel region includes a switching element which is turnedon in response to a scanning signal from a one-side gate signal line, apixel electrode to which a video signal is supplied from a one-sidedrain signal line through the switching element, and a capacitiveelement which is formed between the pixel electrode and anotherneighboring gate signal line different from the gate signal line fordriving the switching element for storing the video signal.

[0058] In this case, to make the above-mentioned capacitive elements inrespective pixels in a pixel row arranged at an uppermost stage or alowermost stage of the liquid crystal display part AR sufficientlyexhibit functions thereof, at a stage above the uppermost stage and at astage below the lowermost stage of the liquid crystal display part AR,pixel rows having the substantially same constitution are formed andthese pixel rows are constituted to be shielded from light by a blackmatrix or the like.

[0059] The respective pixels of the pixel rows which are shielded fromlight by the black matrix or the like are referred to as dummy pixelsand some of these dummy pixels are made to function as theabove-mentioned detection-use pixels DP.

[0060] Embodiment 2.

[0061]FIG. 2 shows an embodiment describing the detailed constitutionwhen light detectors LDA are arranged on an observation-side surface ofa liquid crystal display panel PNL as exemplified in conjunction withthe embodiment 1.

[0062] As described above, the detection-use pixels DP are formed in theregion other than the liquid crystal display part AR separately from thepixels which are formed in the liquid crystal display part AR.Accordingly, usually, in the liquid crystal display part AR, the blackmatrix BM is formed on the liquid-crystal-side surface of a transparentsubstrate SUB2, for example, to define respective pixels, and a materiallayer of the black matrix BM directly extends over regions other thanthe liquid crystal display part AR. The reason that the material layerof the black matrix BM extends over the regions other than the liquidcrystal display part AR is to prevent leaking of light from thebacklight BL.

[0063] Further, in the extension portion of the black matrix BM, holesHL are formed at portions corresponding to portions where thedetection-use pixels DP are formed. These holes HL are formed forpreventing blocking of paths along which light from the backlight BLreaches the light detectors LDA through the detection-use pixels DP by amaterial layer of the black matrix BM.

[0064] Further, with respect to the transparent substrates SUB1, SUB2which constitutes an envelope of the liquid crystal display panel PNL,on respective surfaces of these substrates SUB1, SUB2 which are arrangedopposite to liquid crystal sides thereof, polarizers POL1, POL2 areformed. The polarizers POL1, POL2 are formed such that they extend overthe region where the detection-use pixels DP are formed. The polarizersPOL1, POL2 are required for visualizing the behavior of the electricfield of the liquid crystal and they extend over the region where thedetection-use pixels DP are formed so as to impart the same opticalconditions to the respective pixels in the liquid crystal display partAR and the detection-use pixels DP.

[0065] Further, to form the liquid crystal display panel PNL and thebacklight BL into a module, a frame FRM in which a hole (a displaywindow) which exposes the liquid crystal display part AR of the liquidcrystal display panel PNL is formed is arranged on the observation-sidesurface of the liquid crystal display panel PNL. Here, the frame FRM isformed such that the frame FRM also covers a portion where theabove-mentioned detection-use pixels DP are formed, that is, a portionwhere the light detectors LDA are arranged. This is because that it isnot necessary for a viewer to observe the light detectors LDA with hisnaked eyes.

[0066] Here, a sealing material SL is formed between the transparentsubstrates SUB1, SUB2 such that the sealing material SL sufficientlysurrounds the liquid crystal display part AR. The sealing material SLhas a function of fixing the transparent substrate SUB2 to thetransparent substrate SUB1 and a function of sealing the liquid crystalinterposed between the transparent substrates SUB1, SUB2 hermetically.

[0067] Embodiment 3.

[0068]FIG. 3 is a constitutional view showing another embodiment of theliquid crystal display device according to the present invention andcorresponds to FIG. 2.

[0069] The constitution which makes this embodiment different from theembodiment shown in FIG. 2 lies in that the light detectors LDA whichare arranged at the portions of the detection-use pixels are arranged ona surface of the liquid crystal display panel PNL opposite to theobservation-side surface. Further, for example, sheet-like mirrormembers MM are arranged at the portions of the detection-use pixels DPand on the observation-side surface of the liquid crystal display panelPNL.

[0070] Due to such a constitution, the light detectors LDA can detectlights which are irradiated from the backlight BL and are reflected onthe mirror members MM, wherein since the detected lights are lightswhich pass through the detection-use pixels DP, the optical-system stateof the detection-use pixels DP can be detected.

[0071] Accordingly, it is not always necessary to position the lightdetectors LDA in the direction perpendicular to the transparentsubstrate SUB1 with respect to the detection-use pixels DP. It isneedless to say that provided that an optical path along which the lightfrom the backlight BL connects the detection-use pixel DP, the mirrormember MM, the detection-use pixel DP and the light detector LDA can beformed, the light detector LDA can be arranged in the optical path.

[0072] Here, in this embodiment, in the same manner as the embodimentshown in FIG. 2, the holes HL are formed in the black matrix BM, therespective polarizers POL1, POL2 extend over the region where thedetection-use pixels DP are formed, and the frame FRM is formed to coverthe light detectors LDA.

[0073] Embodiment 4.

[0074]FIG. 4 is a constitutional view showing another embodiment of theliquid crystal display device according to the present invention andcorresponds to FIG. 3.

[0075] The constitution which makes this embodiment different from theembodiment shown in FIG. 3 lies in that in an optical path along whichthe lights irradiated from the backlight BM are reflected on the mirrormember MM and reach the light detectors LDA after passing through thedetection-use pixels DP, the lights are arranged to pass throughpolarization elements PLD which are formed on a backlight-BL-sidesurface of the transparent substrate SUB1. Due to such a constitution,the polarization elements PLD are formed separately from the polarizerPOLL which is formed on the backlight-BL-side surface of the transparentsubstrate SUB1.

[0076] The polarization elements PLD perform a function substantiallyequal to the function of the polarizer POL1 formed on abacklight-BL-side surface of the transparent substrate SUB1.

[0077] In the above-mentioned embodiments, the explanation has been madewith respect to the color liquid crystal display device. However, it isneedless to say that the liquid crystal display device to which thepresent invention is applicable is not always the color liquid crystaldisplay device. This is because that the present invention is applicableto the adjustment of the change of optical transmissivities of anypixels with respect to the pixels of the liquid crystal display panelPNL.

[0078] Further, the above-mentioned embodiments can be respectively usedeither in a single form or in combination. This is because that theadvantageous effects of the respective embodiments can be obtained in asingle form or synergistically.

[0079] As has been clearly understood from the foregoing explanation,according to the liquid crystal display device of the present invention,it is possible to properly adjust the change of the characteristics andchromaticity in spite of the simple constitution.

What is claimed is:
 1. A liquid crystal display device including aliquid crystal display panel and a back light, wherein a detection-usepixel which has the same constitution as respective pixels constitutinga liquid crystal display part of the liquid crystal display panel isformed on a region other than the liquid crystal display part, and theliquid crystal display device further includes a light detector whichdetects light from the backlight through the detection-use pixel and acontroller which adjusts the intensity of the light from the backlightin response to a signal from the light detector.
 2. A liquid crystaldisplay device according to claim 1, wherein a frame having a displaywindow which exposes a liquid crystal display part of the liquid crystaldisplay panel is arranged on an observation-side surface of the liquidcrystal display panel, and the detection-use pixel is covered with theframe.
 3. A liquid crystal display device according to claim 1, whereinthe light detector is arranged on the observation-side surface of theliquid crystal display panel.
 4. A liquid crystal display deviceaccording to claim 1, wherein the light detector is arranged on asurface of the liquid crystal display panel opposite to theobservation-side surface and, at the same time, a mirror is arranged onthe observation-side surface of the liquid crystal display panel in astate that the mirror and the light detector sandwich the detection-usepixel.
 5. A liquid crystal display device according to claim 1, whereinthe detection-use pixels are formed by making use of dummy pixels whichare formed on peripheries of the respective pixels which constitute theliquid crystal display part.
 6. A liquid crystal display deviceincluding a liquid crystal display panel for color display and a backlight, the back light including a red light source, a green light sourceand a blue light source, wherein a detection-use red pixel, adetection-use green pixel and a detection-use blue pixel which have thesame constitution as respective pixels constituting a liquid crystaldisplay part of the liquid crystal display panel are formed on a regionother than the liquid crystal display part, and the liquid crystaldisplay device further includes a red light detector, a green lightdetector and a blue light detector which detect light from the backlightthrough the detection-use red pixel, the detection-use green pixel, thedetection-use blue pixel and a controller which adjusts the intensitiesof the red light source, the green light source and the blue lightsource of the backlight in response to signals from the light detectors.7. A liquid crystal display device according to claim 6, wherein a framehaving a display window which exposes a liquid crystal display part ofthe liquid crystal display panel is arranged on an observation-sidesurface of the liquid crystal display panel, and the detection-use pixelis covered with the frame.
 8. A liquid crystal display device accordingto claim 6, wherein the light detector is arranged on theobservation-side surface of the liquid crystal display panel.
 9. Aliquid crystal display device according to claim 6, wherein the lightdetector is arranged on a surface of the liquid crystal display panelopposite to the observation-side surface and, at the same time, a mirroris arranged on the observation-side surface of the liquid crystaldisplay panel in a state that the mirror and the light detector sandwichthe detection-use pixel.
 10. A liquid crystal display device accordingto claim 6, wherein the detection-use pixels are formed by making use ofdummy pixels which are formed on peripheries of the respective pixelswhich constitute the liquid crystal display part.